As will be referred to in greater detail hereinafter, it is known to employ tension measurement techniques with respect to the adductor pollicis muscle of the human body. Known techniques, however, have involved complicated procedures to achieve the positioning of a force transducer in relationship to the anatomy. Because of difficulties, preference has been shown for the monitoring of electrical potentials in the muscle. This, however, is not deemed satisfactory.
Furthermore, an apparatus and method for detecting the degree of muscle relaxation of a medical patient are disclosed in U.S. Pat. No. 3,898,983 which issued to James Elam on Aug. 4, 1975. Therein is discussed a system and method to indicate automatically the degree to which the muscles of a surgical patient have been relaxed by the use of drugs. In accordance with the Elam disclosure, the electrical pulses are applied to the ulnar nerve which causes the fingers of the associated arm to clench. This clenching is detected by an inflatable bladder which is placed in the patient's hands. When the fingers flex, they squeeze the bladder. The resulting change in pressure of a gas in the bladder is detected by a meter which converts the changes into electrical signals, the magnitude of which indicates the degree of muscle relaxation
The adductor pollicis muscle is the only ulnar nerve supplied muscle, so that there is reasonable assurance that the same muscle mass is excited by voluntary and electrical stimulation. Also, the ulnar nerve is easily accessible for stimulation due to its superficial location at the wrist. The distance the stimulus has to travel is short and does not introduce complexities related to physiological stimulation. The quantitative measurement of the isometric tension produced by one skeletal muscle as a response to the stimulation of its corresponding motor nerve, represents the events occurring at the neuromuscular junction. Therefore, adductor pollicis muscle supplied by the deep branch of the ulnar nerve is most suitable for studying neuromuscular transmission in man.
Previous attempts have utilized responses of the thumb to which the adductor pollicis muscle as well as ther muscles are attached. Because of technical difficulties associated with thumb and hand positioning and immobilization in relation to different transducers and to anatomical differences of human thumb and hand, the monitoring of the potentials from the muscles of the hand has been preferred or the actual movement of fingers or of the thumb produced by multiple muscles of the hand has been measured in the past. These measurements will pick up the gross qualitative changes in the reactions of muscle groups supplied by the branches of the nerve which is being stimulated. However, in none of the previous patents or publications were the conditions for measurement of isometric contraction of adductor pollicis muscle achieved. Therefore, the most important physiological requirement for quantitative measuremnt of skeletal muscle tension was omitted.